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Role of An Expert Witness in DC DUI Cases

If you are facing DUI charges in Washington, DC an expert witness may be called to testify in your case. Below, a DUI attorney in Washington, DC discusses what an expert witness is and how they can be used in DUI cases. For more information on your case, and whether an expert witness may be called in your case, call and schedule a consultation today.

What is An Expert Witness?

Expert witnesses in a criminal cases are witnesses who will be testifying to opinions that are considered outside of the realm of knowledge of an average person. This doesn’t necessarily mean that an expert witness needs to have some advanced degree. Expert witnesses in DUI cases can often be police officers who have simply gained specific knowledge related to certain fields over the course of a short training period. However, expert witnesses in most DUI cases are very important to a prosecutor’s burden of proof.

How Are They Used in DUI Cases?

The prosecution uses expert witnesses in order to be able to provide evidence to either a judge or a jury that a person was under the influence based on certain specialized knowledge. Two very common expert witnesses that the prosecution could call in a driving under the influence case are:

  • An expert on the calibration of a breath testing machine
  • An expert on the administration of a field sobriety test called the horizontal gaze nystagmus test

In the event that the prosecutors call an expert in the administration of a horizontal gaze nystagmus test, they’ll typically use a police officer who had trained to complete the HGN test typically over the course of just one week. The horizontal gaze nystagmus test is a test in which a police officer holds an object, such as a pen, in front of a DUI suspect’s face and moves it back and forth in a specific way, asking the suspect to follow the stimulus with their eyes. What the officer is looking for is involuntary jerking in the eyes called horizontal gaze nystagmus.

Why Call An Expert Witness in a DUI Case?

The reason why the prosecutors need to call an expert witness to be able to testify to this is that horizontal gaze nystagmus is considered to be a scientific test and the average person would not be expected to understand the specifics of this involuntary jerking in a person’s eyes. Even though police officers don’t necessarily receive extensive scientific training and may not have extensive scientific background, their testimony is based on their training to conduct this horizontal gaze nystagmus test.

How Can An Attorney Challenge The Claims of An Expert Witness?

The government experts in a DUI case may not have extensive scientific experience. More frequently in the example of a police officer who’s gotten training in the administration of the horizontal gaze nystagmus field sobriety test, that officer has only been trained for a period of maybe just one week in order to be able to administer that test. That means that a DC DUI lawyer who is extremely familiar with the proper method of administering the field sobriety test can have just as much or potentially even more understanding of the proper way to perform a horizontal gaze nystagmus field sobriety test.

An experienced lawyer will understand when a police officer has conducted an HGN test in an improper manner, such as by looking for the wrong type of clues in the test or conducting the test in the wrong environmental conditions. And in that situation an experienced DC DUI lawyer can challenge the police officer’s administration of such tests.

Additionally, a DC DUI lawyer can also challenge other government experts such as a government witnesses who are experienced in the testing of or calibration of certain toxicology tests. In the event that the government calls an expert in the administration or the calibration of devices like a breath testing machine, a DC DUI lawyer can make sure to request all of the government’s backing documentation used or produced by that expert in order to see whether or not that expert made any mistakes in the calibration process or was not properly certified to even complete those calibrations in the first place.

What Kind of Witnesses Can The Defense Use?

The defense in DUI cases can sometimes call experts to refute the expert testimony of the government’s witnesses. As an example, a defense expert may be able to testify that there are certain other medical conditions that could result in a person exhibiting signs of intoxication even when the person had not consumed any alcohol.

These kinds of experts have scientific knowledge or certain specialized knowledge of conditions that could just as easily result in indicators of impairment but do not involve the consumption of alcohol or drugs or any other impairing substances.

Other experts that a defense attorney may call can include defense experts in toxicology that could help counter the government’s toxicology results and provide refuting evidence as to why a person’s breath, blood, or urine alcohol content may not be accurate in [filtering] the actual level of intoxication that a person may have had when they were driving their vehicle.

How Much Weight Are They Given?

The weight that an expert is given depends on a number of factors. It can depend on the specialized knowledge of that expert has, it can depend on the academic credentials of the expert, it can depend on the manner in which that expert testifies, and it can also depend on how relevant that expert’s testimony is to a given issue.

When there is a defense theory of a person’s DUI case that involves a requirement to call an expert witness, then it’s very important to ensure that the defense is calling a person who is properly credentialed and is able to testify directly to an issue at hand.

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